Northeastern Ordos Basin Research Articles

Continuous unconventional natural gas accumulations of Carboniferous-Permian coal-bearing strata in the Linxing area, northeastern Ordos basin, China

Based on results of laboratory tests and a study of exploration wells, we investigate Carboniferous–Permian unconventional natural gases in lateral extension and vertical sequences in northeastern Ordos basin, China. The primary objectives and techniques are (1) hydrocarbon generation analysis based on Rock-Eval pyrolysis and microscopic observations; (2) reservoir characterization based on depth and thickness extension, nuclear magnetic resonance (NMR) and He porosity/permeability; and (3) gas accumulation analysis based on well cross-sections, field well tests and thermal evolution history.Shale and coal are rich in organic matter and favorable for gas generation, with thermal maturity of approximately 1.4% and shales of type II2 to III kerogen. The gas contents of coal vary from 5 to 20 m3/t with total thicknesses in the Taiyuan and Shanxi Formations of 8–18 m and 4–14 m, respectively, and burial depth increasing from 200 to 2000 m from east to west. Shale and sandstone are also greatly distributed with average total thickness greater than 25 m in both Shanxi and Taiyuan Formations. Porosity is poor for all potential reservoirs, with those of coal, shale, and sandstone being 1.0%–4.9%, 1.0%–1.5%, and lower than 10%, respectively. Three types of unconventional gas accumulations can be distinguished based on differences in source-reservoir combination. The inner source accumulation is composed of coalbed methane (CBM) and tight gas (TG) with direct contact between coal and sandstone, and the strata pressure coefficient (σ) generally varies from 0.8 to 1.0. Close source accumulation is a type of typical continuous TG reservoir with tight sandstone closely related to the source rocks and σ ranging from 0.7 to 1.0. Near source accumulation is relatively distant from source rocks and relies on seal conditions, with σ ranging from 0.4 to 0.7. Due to the gently dipping strata, the eastern area is relatively favorable for CBM development, and the western area is favorable for TG development. Furthermore, shale gas should also be considered in the western area due to good hydrogen generation potential and preservation conditions. Our results are beneficial for the co-production of unconventional natural gas in the entire Ordos basin and other coal-bearing basins.

Geochemical and Preliminary Reservoir Characteristics of the Carboniferous–Permian Coal-Bearing Strata in the Junger Area, Northeastern Ordos Basin, China: Source Implications for Unconventional Gas

Unconventional natural gas development, including coalbed methane, shale gas, and tight sand gas, has received extensive attention recently in coal-bearing basins. This study provides a case study of the hydrocarbon generation potential (coal and shale) and reservoir characterization (coal, shale, and sandstone) of samples from Carboniferous–Permian coal-bearing strata in the Junger area, northeastern Ordos Basin, China. Results show that the coal is dominated by vitrinite (9.3–84.1%) and inertinite (14.0–82.5%) with an average total vitrinite and inertinite content higher than 90% and maximum vitrinite reflectance (Ro,max) values from 0.44% to 0.81%. The shales contain mainly type II kerogen with high total organic carbon content (0.36–31.58%) and relatively low Ro,max (0.45–0.72%). The hydrocarbon generation potential of all the shale samples ranges from 3.25 to 82.82 mg/g rock, and the hydrogen index values range from 100.31 to 768.06 mg HC/g. Three types of fluid inclusions were detected in the microf...

The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China: Reply

We thank Zheng et al. (2016) for their comments on our previous work of sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China (Jiang et al., 2012). Zheng et al. (2016) have different opinions on sedimentary facies and sequence stratigraphy interpretation in the study area. They question our interpretation based on their understanding of sedimentary facies, seismic geometry, orientation of sand body, and sand body thickness. Here, we provide additional evidence to reinforce our interpretation. The structure of this reply follows the order of the questions raised by Zheng et al. (2016). The interpretation of depositional environment for sand bodies in the Upper Pennsylvanian Taiyuan Formation (Ct2) has been controversial for decades. Some previous studies suggested that Ct2 represents a barrier–lagoon–tidal flat system (e.g., Hao et al., 2007; Wang et al., 2007). Zheng et al. (2016) also made such an interpretation. However, northeast–southwest-trending sand bodies in Ct2 were interpreted as fluvial–deltaic channels by many other studies (e.g., Li et al., 1995; Liu, 1998; Fu et al., 2003; Guo et al., 2009; Zhang et al., 2009; Luo et al., 2011). The braided stream fills of the incised valley were documented by extensive erosional surfaces, conglomerate and/or mud clast fluvial lag deposits, and trough cross bedding. Erosional surfaces are one of the most common features observed in cores of Ct2 interval (Figure 1; see also figure 4 in Jiang et al., 2012). The poorly sorted gravels are aligned in various directions, indicating a rapid deposit without significant tidal reworking (Figure 1E). In contrast, the sedimentary structures that Zheng et al. (2016) interpreted as tidal–barrier island signatures, such as mud drapes and cross bedding, can be also found in fluvial deposits. Figure 1. Sedimentary features of fluvial deposit in the …

The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China: Discussion

The paper by Jiang et al. (2012) documented a hiatus and overlying incised-valley fill between the Lower Pennsylvanian Taiyuan Formation (Ct1) and the Upper Pennsylvanian Taiyuan Formation (Ct2). Herein, we provide credible evidence suggesting that the incised-valley fill mentioned by Jiang et al. (2012) is a barrier island. Our work also indicates that the contact between Ct1 and Ct2 is continuous and without hiatus. The Paleozoic Ordos Basin has two stages of sedimentary environments: the early Paleozoic marine carbonate deposition and the Late Paleozoic (Carboniferous to Permian) transformation from paralic to terrestrial. Most scholars believe that the Carboniferous Taiyuan Formation is a barrier–lagoon–tidal flat system (Zhao and Liu, 1990; Hao et al., 2007; Luo et al., 2011) that formed during the relatively large-scale transgression at the North China block. The predominant sedimentary environment of the Taiyuan Formation is the barrier shoreline and has been documented as a barrier island, lagoon, and swamp (Chen et al., 2001; Yang et al., 2005; Hao et al., 2007; Luo et al., 2011). In particular, Jiang et al. (2012) confirmed the facies of Ct1 as a barrier–tidal system and interpreted the interval of Ct2 as a northeast–southwest-trending incised-valley fill and further claimed a hiatus between the Ct1 and Ct2 units. Well D23 locates in the incised-valley fill, as mentioned in figure 14 of Jiang et al. (2012). Its core of the lower Ct2 (above the bottom coal of D23; Figure 1) suggests that it is tidal in origin based on the following sedimentary structures: lens (starved ripples), ripples, and flaser beddings; herringbone bedding; and tidal bundles (couplet) (Figure 1). The fining-upward succession with erosive-based structures of tidal origin is a tidal inlet (Figure 1C, H). The coarsening-upward succession with parallel …

Formation of low permeability reservoirs and gas accumulation process in the Daniudi Gas Field, Northeast Ordos Basin, China

The Daniudi Gas Field is a typical large-scale coal-generated wet gas field located in the northeastern Ordos Basin that contains multiple Upper Paleozoic gas-bearing layers and considerable reserves of gas. Based on integrated analysis of reservoir petrology, carbonate cement C–O isotope, geochemistry of source rocks and HC gas and numerical basin modeling, a comprehensive study focusing on the formation of low permeability reservoirs and gas generation process uncovers a different gas accumulation scene in Daniudi Gas Field. The gas accumulation discovered was controlled by the reservoir permeability reduction and gas generation process, and can be divided into two distinct stages by the low permeability reservoir formation time: before the low permeability reservoir formation, the less matured gas was driven by buoyancy, migrated laterally towards NE and then accumulated in NE favorable traps during Late Triassic to early Early Cretaceous; after the low permeability reservoir formation, highly matured gas was driven by excessive pressure, migrated vertically and accumulated in-situ or near the gas-generating centers during early to late Early Cretaceous. The coupling relationship between reservoir diagenetic evolution and gas generation process controlled on gas accumulation of the Daniudi Gas Field. This study will aid in understanding the gas accumulation process and planning further E&D of the Upper Paleozoic super-imposed gas layers in the whole Ordos Basin and other similar super-imposed low permeability gas layer basins.

Impact of sequence stratigraphy, depositional facies and diagenesis on reservoir quality: A case study on the Pennsylvanian Taiyuan sandstones, northeastern Ordos Basin, China

The Pennsylvanian Taiyuan Formation of the Shenmu Field in the northeastern Ordos Basin of China contains tight sandstone reservoirs that have recently been commercially produced. An evaluation of the reservoir quality of the Taiyuan sandstones will play a critical role in the development of the field. An investigation was conducted to explore possible effects of the sequence stratigraphy, depositional facies and diagenetic alterations on the reservoir quality of the Taiyuan sandstones based on core descriptions, the examination of thin-sections, and core plug and scanning electron microscope analyses. The Taiyuan Formation consists of lowstand system tracts (LST), transgressive system tracts (TST) and highstand system tracts (HST). The LST sandstones are principally medium-to coarse-grained and are interpreted to have been deposited in the dominant distributary channels of a delta plain. The early TST fine-to coarse-grained sandstones were largely deposited in the underwater distributary channel and mouth bar of a delta front, and the middle TST fine-to medium-grained sandstones were deposited in the shoreface to foreshore environment. The HST silt to medium-grained sandstones were mostly deposited in the mouth bar of a delta front and shoreface to foreshore. The Taiyuan sandstones, which are composed of sublitharenites, quartzarenites and litharenites, suffered from extensive compaction that resulted in a large loss of intergranular porosity before the sandstones were further cemented severely. The sandstone cements are mostly composed of illite, ankerite, calcite and quartz. The Taiyuan sandstones have a particularly low average core plug porosity of 7.41% and horizontal permeability of 0.916 mD, which results from that most of the pores of the sandstones are micropores and secondary pores with poor connectivity. The LST dominant distributary channel, early TST underwater distributary channel and proximal mouth bar, and HST shoreface to foreshore sandstones with relatively coarser grain sizes (mostly medium-to coarse-grained) have relatively higher porosities and permeabilities than the sandstones with relatively finer grain size, which is ascribed to a widespread early dissolution by meteor water leaching and lower content of cements within the coarser-grained sandstones. However, the LST dominant distributary channel sandstones had undergone a more effectively early dissolution and less carbonate cementation than the TST underwater distributary channel and proximal mouth bar and HST shoreface and foreshore sandstones had, which lead to the relatively best reservoir quality of the LST dominant distributary channel sandstones among the Taiyuan sandstones. The study revealed that the reservoir quality of the tight Taiyuan sandstones was controlled by sequence stratigraphy framework, depositional facies, grain size and diagenetic alterations together. The sequence stratigraphy framework played a key role in controlling the reservoir quality of the Taiyuan sandstones by governing the depositional facies and corresponding diagenetic products while the grain size affected the reservoir quality of the sandstones by controlling the content of cement within the sandstones.

Understanding the carbon dioxide sequestration in low‐permeability saline aquifers in the Ordos Basin with numerical simulations

AbstractA carbon dioxide (CO2) capture and storage demonstration project was started in 2010 by injecting around 100 000 tonnes of super‐critical CO2 per annum into a set of very low‐permeability sandstone at depths of more than 1600 m in the northeastern Ordos Basin, China. Based on the site‐specific geology and the observational data, a numerical injection model was developed in order to understand the hydrodynamic behavior of CO2 in the subsurface for evaluating reservoir performance. The results show that the model reasonably described the spreading of the CO2 plume. The Triassic Liujiagou sandstone aquifer is the most favorable storage formation for CO2 sequestration at the site of interest. After three years of injection of CO2, the maximum lateral migration distance of CO2 plume is about 550 m and the pressure build‐up is about 13 MPa in the Liujiagou formation for the actual injection simulation. The major storage layer is at depths of 1690–1699 m, which contributes around 80% of injectivity of the entire reservoir system. The leakage of CO2 into the geological seals is negligible (<0.1%) over the entire simulation period. Regardless of the relatively good fit during the calibration period, the model overestimated the pressures associated with the injection thereafter. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Research on Development Characteristics of Ancient Interlayer Oxidized Sandstone in Northeastern Ordos Basin

Research on Development Characteristics of Ancient Interlayer Oxidized Sandstone in Northeastern Ordos Basin

The Geological Characteristics and Controlling Factors of Nalinggou Uranium Deposits, Northeastern Ordos Basin

The Geological Characteristics and Controlling Factors of Nalinggou Uranium Deposits, Northeastern Ordos Basin

Compositions of Zhiluo Formation Sandstone of Northeastern Ordos Basin and its Use as a Provenance Indicator

Compositions of Zhiluo Formation Sandstone of Northeastern Ordos Basin and its Use as a Provenance Indicator

Geochronological Records of Oil‐Gas Accumulations in the Permian Reservoirs of the Northeastern Ordos Basin

AbstractGeochronology of oil‐gas accumulation (OGA) is a challenging subject of petroleum geology in multi‐cycle superimposed basins. By K‐Ar dating of authigenic illite (AI) and fluid inclusion (FI) analysis combined with apatite fission track (AFT) thermal modeling, a case study of constraining the OGA times of the Permian reservoirs in northeast Ordos basin (NOB) has been conducted in this paper. AI dating of the Permian oil‐gas‐bearing sandstone core‐samples shows a wide time domain of 178–108 Ma. The distribution of the AI ages presents 2‐stage primary OGA processes in the Permian reservoirs, which developed in the time domains of 175–155 Ma and 145–115 Ma with 2‐peak ages of 165 Ma and 130 Ma, respectively. The FI temperature peaks of the samples and their projected ages on the AFT thermal path not only present two groups with a low and a high peak temperatures in ranges of 90–78°C and 125–118°C, respectively corresponding to 2‐stage primary OGA processes of 162–153 Ma and 140–128 Ma in the Permian reservoirs, but also appear a medium temperature group with the peak of 98°C in agreement with a secondary OGA process of c.∼30 Ma in the Upper Permian reservoirs. The integrated analysis of the AI and FI ages and the tectono‐thermal evolution reveals that the Permian reservoirs in the NOB experienced at least 2‐stage primary OGA processes of 165–153 Ma and 140–128 Ma in agreement with the subsidence thermal process of the Mid‐Early Jurassic and the tectono‐thermal event of the Early Cretaceous. Then, the Upper Permian reservoirs further experienced at least 1‐stage secondary OGA process of c.∼30 Ma in coincidence with a critical tectonic conversion between the slow and the rapid uplift processes from the Late Cretaceous to Neogene.

Sequence stratigraphy and sedimentary facies in the lower member of the Permian Shanxi formation, northeastern Ordos Basin, China

The Lower Permian Shanxi (山西) Formation is one of the main gas-bearing stratigraphic units in northeastern Ordos (鄂尔多斯) Basin, China. Based on an integrated investigation of well logs, cores, and outcrop, we delineated the sedimentary facies of the lower member of the Shanxi Formation and divided the succession into three third-order sequences from base to top as SQ1, SQ2, and SQ3. The lower region of Shanxi Formation was deposited in the following sedimentary facies or subfacies: subaqueous braided channel, subaqueous interdistributary, mouth bar, swamp and shelf in the Daniudi (大牛地) Gas Field and braided channel, and shelf and lake at Heidaigou (黑岱沟) outcrop. Braided-river deposits form the lowstand systems tract (LST) in each sequence. Braided channels mark the sequence boundaries at Heidaigou outcrop. A shelf and lake depositional environment with dark gray mudstone forms the transgressive systems tract (TST). The location where dark gray mudstone first appears above the braided channel marks the first flooding surface (FFS), and the end of that marks the maximum flooding surface (MFS). The highstand systems tract (HST) deposits are fine-grained sediments with an aggradational parasequence at Heidaigou outcrop and swamp coalbed in the Daniudi Gas Field. Mouth-bar sand bodies in braided delta front, which form the LST in each sequence, form excellent reservoirs in the Daniudi Gas Field.

The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China

The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China

Late Carboniferous‐Early Permian Sequence Stratigraphy and Depositional Evolution in the Northeast Ordos Basin, North China

Abstract:Sequence stratigraphical analysis was applied to the Upper Carboniferous‐Lower Permian sedimentary succession of the northeastern Ordos Basin, north China based on data acquired from ten entire logging curves and eight outcrops. The facies framework of the lithostratigraphical unit, the Taiyuan Formation comprises seven facies in two facies associations, varying from fluvio‐delta to shelf‐barrier islands. The facies are presented within a chronostratigraphical framework, linked by systems tract, which in turn are limited by flooding surfaces and sequence boundaries. Six third‐order depositional sequences are recognised, bounded by six type 2 unconformities. An upwards‐shallowing epicontinental sea sedimentary model is created, which consists of a sandstone, coal seam and carbonate succession.

Study on sequence stratigraphy from benxi to taiyuan formation in Northeastern Ordos Basin

Based on the study of the vertical sedimentary sequence, we recognize the assemblage of vertical lithology, the geochemical test result of mudstone sample, and the characteristics of logs, the sequence stratigraphic interfaces such as regional unconformity, regional tectonic regime interface, sedimentary system interface, transgression surface and so on. Benxi to Taiyuan formation formed in the epicontinental sea, which has subdued floor, so most of the sequence structures from Benxi to Taiyuan formation are duality system tract. Tectonic disturbance, sea level change, and differential compaction provide enough accommodation space for distribution of K1 sandstone and Qiaotou sandstone. At last we establish the framework and model of sequence stratigraphy from Benxi to Taiyuan formation in northeastern Ordos basin in this paper, which contains type model of ramp marginal basin and type of ramp in epicontinental sea background.

Origin and Superposition Metallogenic Model of the Sandstone‐type Uranium Deposit in the Northeastern Ordos Basin, China

AbstractThis paper deals with the metallogenic model of the sandstone type uranium deposit in the northeastern Ordos Basin from aspects of uranium source, migration and deposition. A superposition metallogenic model has been established due to complex uranium mineralization processes with superposition of oil‐gas reduction and thermal reformation.

A sequence stratigraphic model for reservoir sand-body distribution in the Lower Permian Shanxi Formation in the Ordos Basin, northern China

The Lower Permian Shanxi Formation is the main gas-bearing stratigraphic unit in the northeastern Ordos Basin, China. Based on an integrated investigation of well logs, seismic data, cores and outcrops, the lower member of the Shanxi Formation has been subdivided into three third-order sequences from base to top, namely SQ1, SQ2, and SQ3. The three sequences consist primarily of stacked lowstand systems tracts with little deposition of transgressive systems tracts and/or highstand systems tracts. Detailed sedimentological and stratigraphic analyses indicated that the entire sequence is characterized by a regional transgression with incised valleys and channel fills marking the bases of each retro-gradational sequence, and swamp or inter-channel bay mudstone and coal deposits capping each sequence. The three sequences retracted source-ward sequentially from the sandstone-dominated SQ1 to the mudstone-dominated SQ3. The spatial and temporal distributions of the reservoir sandstones was primarily controlled by retro-gradational stacking patterns. Channel sand-bodies formed during the lowstand systems tracts of SQ1, SQ2 and SQ3 are excellent reservoirs, which form excellent reservoir–cap-rock assemblages with the overlying fine-grained sediments. The unique sequence stacking patterns control the accumulation of hydrocarbons. The reservoir quality of the SQ1, SQ2, and SQ3 sequences become worse gradually from base to top. Within each sequence, channel or incised valley fill of the lowstand systems tracts remain potential good expiration targets.